In the oil and gas exploration industry, various techniques of marine geophysical surveying are commonly used in the search for subterranean formations. Marine geophysical surveying techniques yield knowledge of the subsurface structure of the Earth, which is useful for finding and extracting hydrocarbon deposits such as oil and natural gas. Seismic surveying and electromagnetic surveying are two of the well-known techniques of marine geophysical surveying. Seismic surveying and electromagnetic surveying may be used separately or jointly in a survey operation.
During a typical marine seismic survey, a marine seismic source may be towed behind a survey vessel at a particular water depth. The marine seismic source may emit acoustic energy waves in a generally downward direction. The downward traveling acoustic waves may travel through a body of water and be reflected by the underlying Earth formations. The reflected acoustic waves may be detected by sensors such as hydrophones. Information regarding the Earth formations may be derived accordingly.
Generally speaking, when acoustic waves travel through water and Earth formations, higher frequency acoustic waves are attenuated more rapidly than lower frequency waves. Acoustic waves at lower frequencies (for example, infrasound) can be transmitted over longer distances through water and Earth formations than higher frequency acoustic waves. A marine seismic source that produces acoustic energy at lower frequencies may have utility in marine seismic surveys, particularly those conducted in increased water depths.
The design parameters for a marine seismic source may include, among others, acoustic energy output within a low frequency range (e.g., below about 10 Hz), water depth, weight, size and cost. As modern marine seismic surveys continue to explore waters at increased depths, there is a continuing need for a low cost (both in terms of manufacturing cost and operating cost) marine seismic source that produces high acoustic energy at lower frequencies, particularly at a frequency of below about 10 Hz.